Apparatus for the formation of coatings on a substratum

ABSTRACT

In order to build up a thin layer coating on a substratum, a target made of a suitable material and located in the vicinity of said substratum is striked under a high vacuum by a beam of ions of high kinetic energy delivered by a duoplasmatron. Several commutable targets may be used for building up multilayer coatings. An intermediate chamber, located at the exit of the duoplasmatron, may be fed with a reacting gas (oxygen, nitrogen, etc.) in order to obtain compound coatings (oxides, nitrides, etc.).

United States Patent 1191 l lB Bernard Dec. 9, 1975 [5 APPARATUS FOR THE FORMATION OF 3.409529 ll/l968 Chopra et a1. 204/298 COA'ITNGS ON A SUBSTRATUM 3,472,751 8/l969 King 204/298 3,484,358 12/1969 Androshuk et al. 204/298 Inventor: lf q Leon n Toulouse. 3,576,729 4/1971 Sigournay et al. 204/192 rance [73] Ass1gnee: genitreFNatmnal D Etudes Spatiales, Primary Examiner john H. M ack rance Assistant Examiner-Wayne A. Langel [22] Filed: Mar. 21, 1972 Attorney, Agent, or FirmA. W. Breiner [21] Appl. No.: 236,609

[44] Published under the Trial Voluntary Protest Program on January 28, 1975 as document no. [57] ABSTRACT B 236,609.

In order to blllld up a thin layer coating on a substra- [301 Foreign Applicafion Priority Da'a turn, a target made of a suitable material and located M 25 971 F 71 1n the v1c1n1ty of said substratum 1s strlked under a fame [0598 high vacuum by a beam of ions of high kinetic energy delivered by a duoplasmatron. Several commutable {52] 204/298 [ls/491 58 targets may be used for building up multilayer coat- [SI] Int Cl 2 3 21 ings. An intermediate chamber, located at the exit of the duoplasmatron, may be fed with a reacting gas [58] Field of Search 204/l92, 298, 118/491 (Oxygen, nitrogen, etc.) in Order to obtain compound [56] References Cited coatings (oxides, nitrides, etc.).

UNITED STATES PATENTS 5 Claims 3 Drawing Figures 3,408,283 l0/l968 Chopra et a]. 204/298 U.S. Patent Dec. 9, 1975 Sheet 1012 3,925,187

US. Patent Dec. 9, 1975 Sheet 2 of2 3,925,187

APPARATUS FOR THE FORMATION OF COATINGS ON A SUBSTRATUM The present invention is concerned with a process and an apparatus for the formation of coatings, and especially of thin layers, on a substratum.

Thin layers are generally obtained by known processes such as the so-called cathodic sputtering process in which a target, made of the coating material, is striked by high speed particles, the atoms of ejected material being collected on the suitably located substratum, which is generally placed in front of the target and even parallel to it.

According to a well developped process of this kind, a thermionic cathode emits electrons which ionize by collision the atoms of an inert gas, such as argon, and the positive argon ions fall upon the target, brought to a high negative potential, so as to eject its constitutive material and coat the substratum as indicated.

The drawback of this known process is the presence of an appreciable residual pressure to 10' torr) while the thin layer is being built up, and the persistence of a certain amount of plasma around the target and the substratum, which lowers the working efficiency in the layer formation. Besides, this layer may be contaminated by the plasma ions which, while the discharge is established, impinge against the walls of the enclosure.

In the apparatus according to the present invention these drawbacks are eliminated.

To this end the ions striking the target are focussed into a beam directed and accelerated towards the target, under a vacuum of more than 10" torr (and preferably comprised between 10 and 10" torr), which eliminates the above-mentioned drawback.

An object of the invention is to develop an apparatus and a process for building up multiple layers on a substratum, e.g., for the manufacture of semi-conductors, in one single operation during which the vacuum is practically maintained at the same value, indicated above, whereas, in the prior art, the vacuum had to be released, and a manipulation undertaken, after the building up of every individual layer.

Another object of the invention is to develop an apparatus and a process for obtaining easily some coatings made up of several layers of chemical compounds, such as oxides, nitrides, sulfides, etc., by introducing gases, reacting with the target, at a suitable and specially adapted point of the apparatus.

These and other advantageous features of the invention will be more apparent from the following description of three preferred embodiments of the invention, selected only by way of examples, and based, respectively, on FIGS. 1, 2 and 3 of the annexed drawings.

FIG. 1 shows the envelope 1 of an evacuated enclosure inside which a vacuum of 10 10 torr is maintained by a pumping system (not shown) connected at 2. A source of ions 3, preferably a plasmatron or duoplasmatron, known per se, is located at one corresponding end of the enclosure.

This source of ions comprises an oxide-coated cathode 3c, activated by Joule effect by means of heating filaments 4 and 5, and an anode 3A, maintained at a positive potential of 500 V with respect to the cathode, and at a negative potential, adjustable between 5 kV and 30 k\/, with respect to ground.

A highly ionized plasma is built up at the anode level; the ions making up this plasma are picked up by the grounded suck-in electrode 6 located in front and close to the outlet of the ion source.

The ions produced by source 3 and accelerated by electrode 6, impinge, in the form of a well directed beam, on a grounded target 7 facing the beam which is thus entirely intercepted and therefore devoid of any contamination. The atoms ejected from target 7 are collected on a substratum 8 where they build up a thin layer.

In this example, target 7 is perpendicular to the path of the beam and carried by a support 9 cooled by water circulating through pipes 10.

On the other hand, substratum 8 will advantageously be fixed on a heater capable of maintaining temperatures of about 550C during the building up of the thin layer.

The ions produced by source 3 are generally those of an inert gas, such as argon, introduced into the enclosure 3 by means of a suitable device 11 in the form of a capillary tube called a microleak connection. But a reactive gas, such as oxygen, nitrogen, hydrogen sulfide or carbon dioxide (or even carbon monoxide), may also be resorted to, so as to build up a thin layer of oxide, nitride, sulfide or carbide on the substratum.

In the latter case, the outlet of the plasmatron is equipped with an inserted part, called pre-chamber 12, in which said reactive gas is introduced through a conduit 13. This arrangement precludes any reaction clue to direct contact of the reactive gas with the cathode.

By suitably adjusting the ratio of pressure in source 3 and prechamber 12 respectively, concentration of ions in the impinging beam and therefore, stoichiometry of the layers may be varied.

In practice, the target may be a circular one, of about 10 cm diameter, when the diameter of the ion beam will be 5 cm at the level of the target. A rotating diaphragm l4 protects the substratum during the ejection of the first atom layers of the target. Enclosure 1 is connected in 2 to an oil diffusion pumping unit, for instance, (not shown), through an optically tight trap, cooled by liquid nitrogen.

The target is made of high purity tantalum (99.999 Ta). The gases introduced during the discharge have the following purity level argon (99.9995 Ar); nitrogen (99.995% N oxygen (99.998% 0 The connections joining the gas containers with the source of ions 3 are very short and made of copper.

The atomizing or sputtering efficiency will be defined by the ratio of the number of impinging ions to the number of atoms ejected from the target. In the measurements stated hereafter, the number of impinging ions is determined by an accurate computation of the ionic current read from a cylinder of Faraday substituted to the target.

The number of tantalum atoms ejected is computed from the loss of weight of the target. In order to give this computation a sufficient accuracy, the bombardment is sustained for three hours and the loss of weight of the target, in this case, averages 50 mg, the accuracy of the measurement being within O.l mg. The efficiency of tantalum sputtering with argon ions is given by the formula S 0.147 (Am/It) it being supposed that the argon ions were only charged with:

E(kV) S 1.5

Because of the geometrical construction of the apparatus, these values are given for nearly orthogonal impingements.

In the most favourable conditions, the speed of growing of the layer is 1,800 A/ hour, which permits to accurately control its thickness.

It was noticed that the intensity of the beam has in fact little influence on the sputtering efficiency.

Tantalum is deposited on a pyrex substratum, optically polished and previously degassed by heating at 550C for 1 hour. Before the deposition, the target is submitted to a preparatory sputtering by the beam of argon ions to eliminate all superficially absorbed gases.

With an ion acceleration voltage of KeV, drawing an ionic current of 8 mA, the residual pressure inside the enclosure is less than 10" torr.

The layers obtained are strongly adherent to the substratum and show no cavities.

The investigation of tantalum layers by X-ray diffraction shows that:

the layer is amorphous if the temperature of the substratum is less than 200C;

the layer is well crystallised in the isometric phase (face-centered cubes) if the temperature of the substratum is more than 250C.

These results are noticeably different from those obtained with low pressure cathodic sputtering.

The electric resistance of the tantalum layer is measured, during the deposition, by means of two copper contacts previously applied on the substratum.

The thickness of the layers is measured by means of a so called talistep" device. The layers that were obtained showed a thickness of about 6,000 A. ln the case of the isometric phase, i.e., for temperatures of substratum between 250C and 550C, the influence of temperature on resistivity, measured at room temperature, is small. The values of resistivity were found to be comprised between 28 and 32 microhm/cm at C.

The coefficient of resistance was measured between room temperature and 250C. The influence of the temperature of the substratum on the temperature factor is small if the layer is well crystallized in the isometric phase. At room temperature, the coefficient of resistance is 2,200 ppm. by degree C.

It is obvious that the manufacturing process by ion sputtering permits of eliminating many of the impurities; for instance, no phase B, characteristic of oxygen and nitrogen contamination is to be found. The values of resistivity and temperature factor confirm these results.

FIG. 2 shows another embodiment of the invention giving still better results. Target 7 is inclined, preferably by to 45", on the axis of the ion beam, and this arrangement improves considerably the efficiency of sputtering. The substratum 8 is carried by a turntable, rotated by means (not shown) outside enclosure 1. This arrangement enables to deposit several thin layers in one and the same apparatus without interrupting the vacuum.

In a similar way, a multilayer, i.e., a laminate made of several different layers superimposed, may be obtained in one operation, without penetration of air in the enclosure after completion of each individual layer, as it is the case when the targets are changed from the outside.

This is achieved by means of an apparatus according to FIG. 3, in which several (here two) targets 15 made of different materials, are mounted within the apparatus on a common support 17. The ion beam is directed on the selected target in order to build up a layer of coating on substratum 8, then another target is brought into position, in the place of the first, by rotating support 7 by outside means, so as to build up another layer of different composition without interrupting the vacuum.

In a like manner, three or four targets could be arranged.

The apparatus according to the invention is very versatile and particularly suitable for the manufacture of thin and pure layers, of accurately controllable composition and easy to duplicate, which are especially useful in the microelectronics field. Any target of either semiconducting or insulating material may be disintegrated and deposited with this apparatus.

1 claim:

1. Apparatus for forming a thin coating of material on a substratum, including an enclosure which will withstand a high vacuum, said enclosure being partitioned into a first chamber containing a duoplasmatron, an intermediate chamber and a third chamber, said duoplasmatron including activation means for delivery of ions and inlet means for feeding said duoplasmatron with gas, the intermediate chamber being positioned so as to allow the transit therethrough of ions from said duoplasmatron into said third chamber, said third chamber containing a target device, a substratum device, and a set of ion focusing electrodes for directing the ions entering said third chamber to said target whose ejected particles are deposited onto said substratum, and means for supplying from a gas source a gas capable of reacting with the material of said target and a small passage for connecting said gas source with said intermediate chamber so as to introduce a small amount of reacting gas into said intermediate chamber.

2. Apparatus according to claim 1 in which the target means comprises several distinct targets of different materials, each associated with support means for carrying said targets, said apparatus also comprising mechanical means for altering the relative position of the ion beam and of said support means to thereby selectively bring said beam into impingement with any one of said targets.

3. Apparatus according to claim 2 in which said mechanical means and said support means comprise a rotating support for carrying the targets and a driving device for driving said support, which is capable of being operated from the outside of the apparatus.

4. Apparatus according to claim 3 in which the rotating support comprises a cooling system passing through the axis of the rotating support for cooling conjointly all the targets.

5. Apparatus according to claim 1 in which said substratum device comprises several distinct means for supporting substrata, a turntable for carrying said substrata and driving means for revolving said turntable, which is capable of being operated from the outside of the apparatus. 

1. APPARATUS FOR FORMING A THIN COATING OF MATERIAL ON A SUBSTRATUM, INCLUDING AN ENCLOSURE WHICH WILL WITHSTAND A HIGH VACUUM, SAID ENCLOSURE BEING PARTITIONED INTO A FRIST CHAMBER CONTAINING A DUOPLASMATRON, AN INTERMEDIATE CHAMBER AND A THIRD CHAMBER, SAID DUOPLASMATRON INCLUDING ACTIVATION MEANS FOR DELIVERU OF IONS AND INLET MEANS FOR FEEDING SAID DUOPLASDMATRON WITH GAS, THE INTERMEDIATE CHAMBER BEING POSITIONED SO AS TO ALLOW THR TRANSIT THERETHROUGH OF IONS FROM SAID DUOPLASMATRON INTO SAID THIRD CHAMBER, SAID THIRD CHAMBER CONTAINING A TARGET DEVICE, A SUNSTRATUM DEVICE, AND A SET OF ION FOCUSING ELECTRODES FOR DIRECTING THE IONS ENTERING SAID THIRD CHAMBER TO SAID TARGET WHOSE EJECTED PARTICLES ARE DEPOSITED ONTO SAID SUBSTRATUM, AND MEANS FOR SUPPLYING FROM A GAS SOURCE A GAS CAPABLE OF REACTING WITH THE MATERIAL OF SAID TARGET AND A SMALL PASSAGE FOR CONNECTING SAID GAS SOURCE WITH SAID INTERMEDIATE CHAMBER SO AS TO INTRODUCE A SMALL AMOUNT OF REACTING GAS INTO SAID INTERMEDIATE CHAMBER.
 2. Apparatus according to claim 1 in which the target means comprises several distinct targets of different materials, each associated with support means for carrying said targets, said apparatus also comprising mechanical means for altering the relative position of the ion beam and of said support means to thereby selectively bring said beam into impingement with any one of said targets.
 3. Apparatus according to claim 2 in which said mechanical means and said support means comprise a rotating support for carrying the targets and a driving device for driving said support, which is capable of being operated from the outside of the apparatus.
 4. Apparatus according to claim 3 in which the rotating support comprises a cooling system passing through the axis of the rotating support for cooling conjointly all the targets.
 5. Apparatus according to claim 1 in which said substratum device comprises several distinct means for supporting substrata, a turntable for carrying said substrata and driving means for revolving said turntable, which is capable of being operated from the outside of the apparatus. 